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This study tests some of the conflicting predictions made by Grime (1977, 1979) and Tilman
(1982, 1988) on how competition intensity changes along a gradient of nutrient availability.
This was tested by applying three levels of nutrients (fertilizer treatments) and by varying the
amount of neighbors present (competition treatments) in a factorial design using five
common herbaceous species found in the boreal forest understory (Achillea millefolium,
Anemone parviflora, Festuca altaica, Lupinus arcticus, Mertensia paniculata).
Competition intensity indices (CI) were calculated from the final biomass and leaf number
for each species at all fertility levels.
Addition of fertilizer significantly increased biomass and leaf number of A.
millefolium and F. altaica. Anemone parviflora had high mortality in fertilized plots, while
L. arcticus and M. paniculata did not respond to fertilizer treatments. None of the species
responded significantly to the varying amounts of neighbors present in the natural habitat.
Competition intensity (CI) values were not significantly different from zero at any of the
fertility levels for three out of the four species used to calculate CI. The results support
neither of the original predictions made by Grime nor Tilman. However, the lack of response
by these species is consistent with another of Grime's predictions based on his arguments
about the evolution of stress-tolerance: i.e. his so-called 'stress-tolerant' species adapted to
live in habitats of extremely low resource availability.